VIENNA- An apparent delay in Iran's building of a nuclear conversion plant suggests its stockpile of low-enriched uranium (LEU) gas will grow for a while longer, despite Tehran's deal with world powers to curb its disputed atomic activity.

Among other steps, Iran agreed under the six-month accord - which took effect on Monday - to limit its LEU reserve. The new plant is meant to achieve that by turning the material into oxide powder that is not suited for further processing into high-enriched - or bomb-grade - uranium.

Diplomats and experts said the matter was of no immediate concern since Iran's commitment concerned the size of the stockpile towards the end of the deal, in late July, giving it time both to complete the facility and convert enough material.

But one Vienna-based envoy said Iran's progress in building the conversion line would be closely watched as part of the implementation of its obligations under the accord with the United States, France, Russia, Germany, Britain and China.

"It will be a problem if the facility is not completed in the next few months," Mark Fitzpatrick, director of the non-proliferation programme at the International Institute for Strategic Studies (IISS) think-tank, said.